Splais,
This "It ran great one day and Dead as Door nail the next" is most likely electrical. Like Pat says timing will run the motor even it its out of whack (of which it might whack you pretty hard) The carb doesnt care if the crank runs forward or backward as long as the piston/ring assy provides pressure. The dead syndrom has to be an intermitten short some where.

Ive seen
1. Known good packs have an internal break in the solder/spot weld on the strap and cause the above syndrom but one day the die in the air.
2. Most people equate electrical problems with Carb problems, when in doubt dont tear up the carb until your sure.
3. Rcexel ignitions are great things but sometimes they spark but won't run the engine, however most of the time they fire one time and that's all they do, never seen one totaly dead one day then run the next but you never know.

Good Luck

jds